This invention relates to surgical bone cement compositions and more particularly to bone cement compositions having anaesthetic properties, and to methods for producing local analgesia.
Polymer based surgical bone cements have been used for many years to fill voids in bones and to improve fixation of implanted orthopaedic prosthetic devices. Typically such cements contain polymers or copolymers of alkyl methacrylate and/or copolymers of methyl methacrylate with methyl acrylate or styrene. The liquid compound consisting of esters of acrylic or methacrylic acid (typically methyl methacrylate) is packaged in an ampoule, possibly with additives such as premature polymerization preventers such as hydroquinone, and curing promoters such as N,N-dimethyl-p-toluidine. A polymerization initiator, typically an organic peroxy compound such as powdered benzoyl peroxide, is combined with the polymeric component and radiopacifier (such as barium sulphate or zirconium dioxide). The polymeric materials are generally sterilized by either irradiation or gas sterilization. In use, typically a bone is cut and prepared to receive a surgical implant and then the liquid and dry components of the cement, contained in the ampoule and a powder bag are mixed together to form a paste which can then be applied by the surgeon to the cut bone. The implant can then be set in the paste which, when fully polymerized, forms a continuous solid interface between the implant and the bone.
It is also known to incorporate therapeutic or diagnostic substances into the bone cement for various purposes. For example, U.S. Pat. No. 4,900,546, issued Feb. 13, 1990 to Poseyn Dowty et al, teaches the incorporation of antibiotics such as gentamycin, penicillin and tetracycline; anti-cancer drugs; anti-inflammatory drugs; immuno-stimulants; immuno-suppressants; osteogenic promoters and diagnostic substances such as radioactive tracers. While anti-inflammatory drugs may be defined as analgesics, such compounds are not anaesthetic agents.
Although local anaesthetics, such as lidocaine and prilocaine are known to have potent anti-microbial activity (anti-bacterial and anti-fungal), when used in relatively high dosages (0.5-2% solution) (J. Infect. Diseases, Vol 121, No. 6,597-607, June 1970), heretofore such anaesthetic compounds have not been incorporated into bone cements for the promotion of anaesthesia. It has now been found that substantial pain relief can be achieved by incorporating into a known bone cement composition a local anaesthetic agent at a dosage level several orders of magnitude lower than would be required to achieve an anti-microbial effect with such agent.
An object of the present invention is to provide novel bone cement compositions, having anaesthetic properties, which incorporate an analgesic. Another object of this invention is to provide a method for producing analgesia adjacent to a bone end.
By a broad aspect of this invention, there is provided an anaesthetic bone cement comprising a bone cement composition including an effective amount up to about 5% by weight of a local anaesthetic agent.
By a preferred aspect of this invention, there is provided an anaesthetic bone cement composition comprising: (a) a liquid monomeric (meth)acrylate composition; (b) a powder comprising at least one of a homopolymer and a copolymer of methyl methacrylate containing an effective amount of a polymerization initiator and a radiopacifier; and (c) an effective amount up to about 5% by weight of said bone cement composition of a local anaesthetic agent.
By another aspect of this invention, there is provided a process for the production of an anaesthetic bone cement comprising combining: (a) a liquid monomeric (meth)acrylate; (b) a powdered component comprising at least one of a homopolymer and a copolymer of methyl methacrylate, an effective amount of a polymerization initiator and a radiopacifier; and (c) an effective amount up to about 5% by weight of a local anaesthetic agent.
By yet another aspect of this invention there is provided a method for producing analgesia at an orthopaedic implant site in a patient, comprising cutting and preparing bones at said site to receive said implant and applying to said prepared bones a bone cement composition comprising: (a) a liquid monomeric (meth)acrylate composition; (b) a powder comprising at least one of a homopolymer and a copolymer of methyl methacrylate containing an effective amount of a polymerization initiator and a radiopacifier; and (c) an effective amount up to about 5% by weight of said bone cement composition of a local anaesthetic agent.